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Why do commercial helo pilots wear helmets?
I've been on my fair share of commercial helo rides, primarily in Canada.  Over the course of more than ten rides in three different kind of helos (Bell 407, 412, and I think one other) there was only one time when the pilot wasn't wearing a helmet.
It's worth noting that these flights were taking off and landing in very remote areas of the Selkirk mountains, usually on glaciers.
At the same time, I have been around (US) flight schools since I was 15 years old, and I've never seen an instructor or student helo pilot (flying R22s and similar) wear a helmet.  Also, fixed wing pilots don't wear helmets.
Why do commercial helicopter pilots wear helmets, when instructors and students don't?
It's a little hard to see, but here's a photo of one of the choppers, and you can see that the pilot is wearing a helmet.

The same reason as anyone would wear a helmet - to protect their cranium in circumstances when there is the possibility of damage to that area of the body.
Helicopter operations are often low level, sometimes over dangerous terrain and, unlike fixed wing aircraft, they do not have the option to glide away from an engine failure. Low-level operations may not afford the pilot the altitude required for a successful autorotation landing so there is the possibility that they will be going down hard and fast.
Taking an example of low-level flight over forestry resulting in a forced landing, this may be survivable, but the pilot will be thrown around quite a bit as the aircraft is buffeted by the trees as it goes down. Some head protection would be important to the survivability of this crash.
There are a few other reasons I could think of apart from the main one above

Some helicopters operate with doors open, up where the birds fly around. A seagul to the head would not make for a happy flight
Noise - helo's can be louder than Fixed wing and the helmets could provide better noise cancelling
Specialist helo operations such as S&R use equipment such as night vision, which could be mounted on a helmet
Habit - ex-military helicopter pilots could just be in the habit of wearing a helmet, and carry this over to civilian operations.

True Story: One day out on LRRP patrol, my unit heard over the radio that our evac chopper was grounded due to an in-flight emergency; they'd suffered a bird strike. Turned out our Colonel had been hit by a Kestrel. Our Col carried a pet ferret in the cockpit and the Kestrel had evidently waited until he banked the chopper hard over preparatory for a dive down to follow terrain into the lz; the Kestrel chose that moment to dive in for the damned rodent. Bird 0 Ferret 1; Pilot had severe lacerations of his right arm. He caught hell for years and his call sign ended up changing because of it.

All these points except that two also seem to apply to students and instructors, right?

Obviously they wear a helmet for safety, but is commercial helo pilots do, why don't student pilots?  There are probably more student accidents that commercial ones?  Not to mention: I've landed on non-runway (dessert) terrain in FW aircraft, and I've never worn a helmet.

@kjmccarx Student pilots have the lowest accident rates since they are accompanied by an experienced instructor how can take control as needed.  They only fly solo when ready and then only in "easy" conditions and flights.  Mid-time PPLs are the next most at risk followed by commercial pilots who simply by virtue of them spending significantly more time in the air and more time in the areas of hazardous operations that PPLs do not enter or if they do, only for short periods of time.

@raptortech97 I don't see any reason for flying with the doors open while learning to fly so I would guess the first one wouldn't apply, either.

@kjmccarx - I would suggest student pilots don't for the exact opposite reasons given in the answer. ie, they dont fly risky/low as some commerical operations do, they're not in the habit of doing so, they're not flying door open, they dont have special eequipment that needs a mount etc etc.

@DavidRicherby we fly with the off during training because its hot, especially hovering in a glass bubble in 100F heat for an hour. usually only the door on the opposite side of the tailrotor is taken off, to prevent, say, a chart from hitting the TR

Not having a place to auto into is not a failure of the helicopter, any more than not having a place to land in a low-level failure of a FW. It's a pilot failure. Secondly, many copters doing low-level operations are twins, unlike FW.

I've purged a bunch of comments. Further discussion of this answer (and Stack Exchange policies on editing in general) should take place on Meta, not in the comments.

You have 2 distinct questions. In answer to the "Why do commercial helicopter pilots wear helmets, when instructors and students don't?" as well as the implied "Why do Canadian Pilots Wear them when American pilots do not"
From what I can tell, a large part of the American industry is either "lower risk", Multi-engine flight from airport to airport, or passenger oriented, i.e. Tour pilots, Offshore pilots. In Canada, while there are still Tour pilots, and pilots flying airport to airport, both will, over the course of their job, fly over much more remote terrain, routinely preforming off airport landings in remote, unprepared landing spots. One of the techniques used in Canada  more often than other countries is Long Lining. Not only do the doors often come off for better downwards visibility when doing this it also is more risky than normal flight.
As to the part of your question regarding why some pilots do not wear helmets, rotary wing aircraft have a significantly higher chance of crashing than a well maintained commercial fixed wing aircraft. As far as American flight instructors not wearing helmets, it is probably down to culture, I have read some people arguing that the instructor wearing a helmet scares potential customers. Inversely I am aware of at least 1 Canadian flight school witch provides students helmets as part of there commercial training. There may also be a link to the fact most Canadian Instructors are experienced Pilots, while the US industry uses mostly brand new pilots as instructors.
Jamiec's Reasons are the answer to the question in your title
Reasons not to wear a helmet might include:

Uncomfortable and/or Hot
Cost: about $1500 and up
Looks [worry’s about intimidating customers]
Simple belief they are not necessary

I was wondering if simply "the loudness" is a reason to wear a helmet - do they help block noise (even more than large over-the-ear headsets?)

Having now tried a helmet in a helicopter, as well as a few over ear headsets, the helmet is no better at blocking normal noise than a good set of noise canceling headphones, some say its actually worse. an exception would be when needing your head outside the aircraft where the helmet blocks wind and to some extent the much high pitched turbine noise.

cool info !  cheers..

Lots of Offshore helicopter pilots wear helmets and so do most of military pilots. Since (historically) helicopters have a higher rate of accidents than similar class airplanes, any hard landing or a survivable crash would result in violent shaking of crew, probably knocking them unconscious if their heads strike the confined cockpit's superstructure. Helmet would save them from this and increase their chances of survival. This is more so over sea as getting out of a ditched helicopter requires quick reactions- thus being fully conscious is so important!


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Why are thrust reversers so unreliable?
I see many questions regarding the unreliability of thrust reversers. Why are these components so faulty across all airplane models and manufacturers?
Is there a technical challenge to making the the thrust reversers as reliable as other aviation systems? Are the A380's electronic thrust reversers more reliable than the traditional mechanical or hydraulic reversers?

There is redundancy just like nearly everything in aviation. Though you may wish to reselect your examples only 1 the crash is about unreliability.

I think there is a fallacy in the basis of your question. Your first and third links to not point to questions about unreliable thrust reversers.

Are they really unreliable?  In my experience I flew with an inop thrust reverser about 0.25% of the time.

@casey: I drive my automobile twice a day, six days a week, at a minimum. Therefore I rack up 400 drives in about a month to a month and a half. Any component that I find is inop on the vehicle monthly I would call unreliable. Are airplanes held to a lesser standard?

@dotancohen I operated between 20 and 50 flights per month generally. Less on average when you consider training months, leaves and vacation. Racking up 400 flights took a while. Also note the fleet flew more than 3000 hours per day.

@casey: I see, the standards for automotive (arbitrarily picked as a generally familiar transportation category) differ from that of aviation. The reasons for that are clear, as in a comment to reirab below, that airliners are operated by professional pilots who train for such conditions.

I would also like to mention that in rereading my earlier comment, it may come across as having been a bit rude. That was not my intent! I very much appreciate your input and your willingness to share your knowledge! I simply found the numbers vastly different from what I was expecting, not only for the TRs, but for all aviation components in general (in which it seems that the TRs are not extraordinarily unreliable).

It's not so much that thrust reversers (TRs) are more unreliable than other components of the plane. However, they have a very important impact on the airplane's performance. Hydraulics, flaps, and even engines fail regularly. But engines and hydraulics can be backed up by redundant systems, and an airplane can still land without flaps. But engineers learned from Lauda Air Flight 004 that an airplane may not be controllable if the TRs deploy in flight.
So in the interest of safety, the TRs have additional precautions. The reasons for not aborting a landing after they are deployed are discussed in your first linked question. Reliability is also not the only reason for having no TRs on the A380 outboard engines, as discussed in the second linked question.
So to answer your question, there is indeed a technical challenge in making the TRs reliable: they absolutely must not deploy in flight. This means many safeguards are put in place, and they are designed to fail by not deploying if there is any doubt about whether it is safe. A TR that won't deploy is more desirable than a TR that deploys when you don't want it to.

I would disagree with the assertion or assumption in the question that TR's as "so faulty" and significantly less reliable than other systems.  Based on my experience, the reliability of TR's is probably between 99% and 99.9% -- in other words the times when a TR fails to work is between 1 in 100 and 1 in 1000 flights.  That, to me, doesn't look like a particularly bad record.
Modern aircraft in general are extremely reliable, so when you compare a component with a 99.x% record against a component with a 99.999% record (say, a windshield -- how often do you see those fail?), the former doesn't look good in the comparison.  But when you consider that there are thousands of commercial flights daily in the US, and it's uncommon for anything significant to make the news, the reliability rate for the system as a whole is extremely good.
Some of this is fault tolerance; on most runways, unexpected loss of a TR doesn't affect things very much.  The vast majority of the time, braking performance is entirely adequate to stop the aircraft well before the end of the runway even with no reverse thrust (not merely one of two or one of four failed).
But in over a decade of flying modern jet aircraft, the number of times I've seen a TR fail to deploy I could probably count on the fingers of one hand, so all in all I'd suggest that they tend to be quite reliable.

Regarding your 3rd paragraph, braking performance alone is always sufficient to stop the aircraft without reverse thrust. This is a requirement. If the runway isn't long enough to land and stop safely w/o reverse thrust, you can't land there (except, of course, for the standard caveat of emergency situations.)

@reirab -- That's not correct.  It is legal to land on a runway where contamination etc makes the conditions such that operative TR's are necessary to stop.  That legality may reside in an OpSpec, which differs from one carrier to another, but the 'requirement' you mention is NOT universal.

The one valid failure example from the original question isn't a failure to deploy, its an uncommanded deployment in flight - a situation that's been rectified in the ensuing 24 years. However, I'd still agree with you that they don't seem any less reliable than other systems.

@RalphJ Ah, good point about contamination. I was thinking of a dry runway. The FAA does indeed require the assumption of inop engines when computing dry runway landing field length (FAR 25.125(f).)

Thanks, Ralph. In automobile terms, a 1/1000 failure rate is considered high. That would mean the same component in your car breaking every three to four months. But I understand that airliners are operated by professional pilots who train for such conditions, which sadly cannot be said of general passenger automobile failures.

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Can anyone help me identify the plane in this photograph?

I'd be very grateful for any help in identifying this U.S. plane. Other photos in the album look like they're from WW2.

could you post more photos on imgur?

It looks like a Ford Tri-Motor

Depends on how accurate do you want to detect it and how will you use it?
The simplest way is to build horizontal line filter to identify wings position, build contours, filter out only the biggest and most horizontal ones and then wrap them with the rectangle. This will be the biggest part of the plain, won't it?

@dmitry.kresin I'm not sure if you're joking but this is my favorite comment of the day.

Ford trimotor is a High-Wing monoplane, that in mage looks a biplane. A model often mistaken as a Ford is the rare trimotor built by Fokker of The Netherlands, a propaganda movie about the anarchists in Spanish Civil War: 'Aguiluchos de la FAI en tierras de Aragon', shows a Fokker.

What you have there is I believe a Boeing Model 80A-1:

Source

Source
You can read more about it on Wikipedia: Boeing Model 80
The Model 80 air transport aircraft was built in the mid 1920's. It is notable as being the aircraft used for the first flight to feature a flight attendant, which were registered nurses at the time.

@QPaysTaxes No, I searched google images for "3 engine biplane" then scrolled until the first picture in my answer showed up. The Model 80 showed up sooner, but the early Model 80's did not have a tri-tail design so it threw me off a little bit.

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Strange plane-shaped object at UK airport
A friend sent me the following image, spotted at an UK airport. Do you have any idea what that might be?
It looks a bit like MD-11/DC-10 transport case, but i have no idea. Is something like this used to transport airplanes?

related, if not duplicate: https://aviation.stackexchange.com/q/26968/1467

That's a training rig for airport fire crews. They can usually be set on fire through whatever controlled means and the crews can practice approaching and working around aircraft.
In fact, after a cursory Google it's either the one at Heathrow or is near identical to it.

No need for being almost positive; that's what it is.

Maybe Heathrow has one as well, but it looks like the one at Stansted too - https://www.google.co.uk/maps/place/Stansted+Airport,+Stansted+CM24+1RW/@51.8873242,0.2326068,162m/data=!3m1!1e3!4m5!3m4!1s0x47d88e5e1bd094c3:0x1438d71a4733b651!8m2!3d51.8899385!4d0.2617407

More views of a fire simulator can be found on Heathrow's photo library: fire simulator.

That will be a fire trainer, for the airport fire fighters to practise procedures for different types of fire and smoke events. Here's the one at Amsterdam Airport:
Image source
Some of the fire trainers, if not most, have a replicated interior as well so that procedures can be trained for going into the plane, in realistic heat and smoke circumstances.

This is a dummy aircraft used for training firefighters. I believe that it's coloured green so that random observers don't think that it's a true emergency.


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Why are outward-opening doors heavier than plug-type door in a plane?
I saw on LinkedIn:

Why are outward-opening doors heavier than plug-type door in a plane?

Both of those are plug-type doors, so I wouldn't be too confident in the credibility of this source. The Airbus design might be heavier though...

The source is nonsense. It might be more AI drivel. The Airbus door does not rely on mechanical locks, it too relies on air pressure. Boeings do have assist unless it's a 737. I too believe the Airbus style can be heavier due to load being concentrated at the door stops.

@Bianfable, "Both of those are plug-type doors..." Huh?  They both open outward, not inward... what am I missing here?

They both open outward and are plug-type. The exact motion is a bit more elaborate. Some details are in this answer, including links to videos showing the mechanism in more detail.

@Bianfable The reference calls the A321 a plug door but it is not. It has pins that slide into catches as the door drops into its sealed position from the outside. In contrast, the Boeing door tilts and angles so as to enter the fuselage then reorients itself to close from the inside. Pressure tries to open the Airbus door, working against the pins where pressure forces the Boeing door tighter into the frame.

There is nothing wrong with this question other than the table says a plug door is the heavier, which is backwards. Bianfable's reference shows the operation of the airbus door. Contrast that with this Boeing video. https://www.youtube.com/watch?v=cxzLNBlDVbE

Plug type:
Self sealing door. The cabin pressure forces the door into the fuselage. As long as the door is larger than the opening (with proper shape and strength) only minimal hardware is required to keep it from becoming dislodged.
Outward opening:
Not "self sealing". Additional hardware and fortifications are required to keep the door from busting open.
Note:
If your airline is pressurized to the equivalent of about 8000 ft altitude, the pressure differential is 4.2 PSI for an aircraft at 36,000 ft (10.9 - 6.7). I don't know how big an airline door is, but this equals about 600 lbs force per square foot. This force is mostly concentrated on the hardware used to hold the door on, hence a lot of fortification is required.

The doors in the question's picture are both plug type and both open outward... And they are neither castles needing fortifications  Is this an AI generated answer?

Still a valid question even if they picked a bad picture. What makes you think this is AI generated?

All questions are legitimate  But this question is asked like if outward opening doors and plug doors were mutually exclusive which is not the case. It also refers to a link and a picture which are confusing as well.

The wording from Part 25.783 is "initial opening movement is [not] inward." The Airbus style door has an initial opening movement that is inward, and thus is "self sealing." Most hinged airstair doors on regionals and even many outward bulk cargo doors, meet this opening inwards requirement.

@user71659 The Airbus door is not a plug door and you misinterpret its initial movement. It is held in place by pins and seals on the outside. If the pins break the door will fly off. The characteristic of a plug door is that it jams itself into the fuselage frame, and the wall of the aircraft has to break before it will fly off. This is a reasonable answer.

@sophit It seems reasonable that fortification means reinforcement. The A321 door is not a plug door, regardless of the description. Look at its operation. This answer is correct.

@Pilothead Incorrect, I suggest you review how the Airbus door works. The door stop rollers fit in tracks that are shaped like a 7. This means the door has to go back before it can lift up and clear the roller track and static stops. You also need to read my comment carefully. I never claimed it was a plug door, nor does Part 25 say anything about plug doors, only the initial movement of the door.

@user71659 This whole question is about plug doors and whether or not they are heavier than non-plug doors, labeled outward opening. If you are arguing that the label is not sufficiently descriptive, then ok. Arguing that any door with initial inward movement is self sealing is not correct. It only means that the latching mechanism has over center like operation. If the latch breaks, the door still comes off, ie. not sealed. The presence of latches (or not) and the required reinforcement to make them work is the difference between the categories of door, and the essence of the question.

@Pilothead: both doors are subject to more or less the same pressurisation load. Boeing's door download that load via its "wider than the hole" sides pushing against the fuselage frame; Airbus's door download that load via rollers/pins also pushing against the fuselage frame. Being both systems sized by the same load, that all the pins on the Airbus's door will break is as probable as that the "wider than the hole" sides of Boeing's door will break. I wouldn't expect one design to be more complex, heavier, safer or cheaper than the other one but I agree that the terminology is misleading.

@sophit I admit I don't know exactly how Boeing's "wider than the hole" door is designed, but it could potentially distribute the load around the entire perimeter of the door. The airbus door, using pins, has far less surface area to distribute this same load. Since pressure = force / area the Boeing door could potentially get away with FAR less fortification.

@codenoob: Yes, the fuselage frame around the door of an Airbus might be reinforced where the pins engage but the rest of the structure might be built thinner so that saying that globally one design is lighter than the other is a bit difficult.

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FAA PPL certification for indian nationals
I am looking to acquire a FAA PPL certification. I have a B1 visa and I am getting conflicting advice on whether I can get a PPL certification in the USA.
Some people/websites say that a B1 visa is adequate and some others say that without a M1 visa, I can only get training but not the certificate. I have checked with Treasure Coast Flight Training in Florida and received less than satisfactory response (from their Indian rep).
I would like to complete the training at the shortest possible time period. If anyone can clarify what kind of visa I need and, perhaps more importantly, direct me towards a flight training school suitable for my needs, I would be obliged. At 57, I do not have the luxury of waiting indefinitely; especially, since I am planning to use this certification (and any possible networking within the flying community) to start my next business.

Hi, unfortunately ressource location it out of scope for aviation stackexchange, for this reason this question might get closed... But out of curiousity, why do you not get your PPL in India? Would that not be easier/cheaper?

"I am planning to use this certification [PPL] to start my next business."  In India, or the US?  If US, I trust you have researched the privileges and limitations of a PPL?  As well as work vs training visa requirements?  (presuming they might be different...)

U_flow, hope I get some answers to my question before our gets taken out.

If you are in the US on a B1 visa, only study that is "avocational or recreational in nature" is allowed, per the Who Can Study? document published on ICE's website, and it must be incidental to the purpose of your visit.
While one could argue that taking a few flight lessons could be "recreational," it's hard to imagine that argument working for an accelerated course of study culminating in a certificate that will be used for business. You almost certainly need to apply for a change in visa status for that to be kosher.
All that said, you should stop relying on random internet sources (me included!) Contact the US State Department directly for any questions you have.

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Why does a Cessna 172 have dihedral wings if it has high wings?
"Dihedral goes hand in hand with low wing aircraft, and anhedral goes with high wing". This is what I assumed till now.

But when I see a Cessna 172, the wings are a little dihedral. So why does it need more lateral stability? Or is the lateral stability more pronounced with the weight of the aircraft (comparing with Antonov An-225 Mriya)?

Do high-wingers have dihedral? only talks about whether they have or not, or what dihedral does, which I knew already. Thanks to John K, now I understand the relation of swept wings and dihedral effect better.

@DigitalDracula thank you for the link, but it did not.

Congratulations on writing a post which manages to meaningfully put the Mriya and the Cessna-172 in a single post :D

The vast majority -- perhaps 100%- of high-wing light airplanes do not have anhedral!

The dihedral effect is an opposing rolling moment induced by a sideslip.  When an airplane is disturbed from wings level, it immediately starts to slip "downhill", slide sideways toward the low wing, in effect.  The vertical fin starts to react to this after a certain amount of slip has developed, to realign the airplane with the airstream, weathervaning it more or less, and the airplane turns (while going downhill, unless you increase angle-of-attack.
The fin needs to be small enough to allow this slip to develop a small amount for dihedral effect to work.  The slip generates the rolling moment to restore level flight, and there's your lateral stability.  If the fin is too big, it will start to weathervane the plane too soon, and dihedral effect can't develop strongly enough to roll the wings level, and the plane instead wants to spiral right away.
Anyway, you get dihedral effect from three configurations that can generate rolling moments from sideslip: geometric dihedral (wings angled up), the T intersection of a high wing configuration (where diagonal flow is unhindered across the roof, but is blocked by the fuselage below, increasing the lift on the low wing), and wing sweep.  High wing airplanes may get enough dihedral effect just from the T configuration, and the wing can be straight, especially if maneuvering is a higher priority than cruising.
The Canadair CL-215 has no geometric dihedral; the T junction is sufficient for a water bomber that makes maneuvering a higher priority than cruising (when the CL-415 was tested, the flat engine nacelles sticking up were like fences that inhibited lateral flow, as if there was fuselage extending above the wings, and resulted in killing off much of the dihedral effect of the T junction; the odd turned up wingtips of the 415 are "dihedral plates" a band-aid designed to restore dihedral effect for the desired lateral stability).
In the 172, (and probably most high wing unswept aircraft designed for cruising), Cessna wanted to supplement the dihedral effect of the T configuration with a bit of geometric dihedral to get the total effect they wanted. The geometric dihedral is probably about half the angle of a low wing airplane, since no more is necessary thanks to the high wing placement. High wing transports with unswept wings, like the Dash 8 family, have a small amount of geometric dihedral as well, maybe a degree or so outboard of the engines, to supplement the dihedral effect of the T configuration.
This brings us to wing sweep. Wing sweep generates really strong roll due to sideslip (something you find out pretty fast when you take a jet initial type rating), so there is strong dihedral effect from sweep. When the wing is at the top, you have the dihedral effect of the T configuration, plus the dihedral effect of the wing sweep, and you get way too much roll due to sideslip for desirable lateral stability and dutch roll characteristics.  To reduce the excessive dihedral effect, they use anhedral to reduce the total roll/yaw coupling effects to a desirable level.
That's why almost all high wing aircraft with swept wings have anhedral (to basically cancel out some of the effect of the sweep), whereas high wing airplanes with unswept wings have zero or mildly positive geometric dihedral.  Likewise, a low wing swept wing jet will have less dihedral than it would have if the wings were unswept.

in doing research with uncontrolled high aspect free flight monowing models, it was found that a side wind gust actually rolled the plane away from the wind faster than the tail fin could turn it into the wind.  One solution was to keep the wing dihedral, but put more "anhedral effect" area under the CG.  Amazingly, dihedralled biplanes of similar wing area performed better in crosswinds.

"When an airplane is disturbed from wings level, it immediately starts to slip "downhill", slide sideways toward the low wing, in effect. " -- in my opinion the cause of sideslip when an aircraft banks is complex, and intimately related to the fact that banking causes turning, and is best not viewed as being driven by the gravity vector or tending to involve a loss of altitude. The idea that gravity tends to pull a banked aircraft sideways through the air toward the low wingtip, thus causing a sideslip, is a fundamentally an Aristotelian perspective.

Btw, this viewpoint has become widespread in hang gliding training, and the error has been further compounded via an additional faulty leap of logic, which claims that the way to prevent or minimize sideslip while turning (in a rudderless aircraft) is to adequately "load up" the wing during the turn entry by increasing the angle-of-attack (moving the control bar forward). In reality I've found that an accelerating (airspeed-increasing), diving, low-G style of rolling in to a turn, while rather exciting, actually involves no more sideslip than a more "correct" ("coordinated") turn entry.

In many cases (including the hang gliding case, and most light aircraft when being flown w/o use of the rudder), roll rate is by far the dominant driver of sideslip.  In some light aircraft and especially sailplanes, aileron position can also be a strong driver of sideslip, thus allowing constant-heading constant-bank sideslips w/ pilots feet off rudder pedals.  Obviously, for dihedral or high-wing position to have the effect that it does, bank angle can also be a driver of sideslip, but the point of these comments is that the mechanism for this is not as obvious as it may first appear.

When you tilt the lift vector by banking, a horizontal component is added to the lift.  This is more or less perpendicular to the direction of travel, so the airplane slews sideways.  It's no different than when hovering a helicopter and you tilt the rotor left with left cyclic.  It moves sideways, and if also going forward, it's moving ahead and sideways.  The fin's weathervaning effect is what induces the actual heading change.  The hang glider also slips sideways when it banks, but the weathervaning effect is still there to create the heading change, built into the wing sweep.

From your examples, the Cessna 172 is "in between".
One key to understanding this is vertical Center of Gravity and how the plane behaves in a slip. Dihedral can be added to help roll away from the relative wind, as can a tall vertical tail fin or any area above the CG.
But the main function of dihedral is for roll stability in straight line, unaccelerated flight, ie. cruising.  A little nudge from a gust or turbulence will be damped by the momentary offset of the center of vertical lift and the center of gravity.  That, and any ensuing side slip, will tend to roll the plane back upright.
Any plane that has to build in anhedral, such as a massive cargo carrier, does so because it is excessively sluggish in roll.  In smaller aircraft, aerodynamic effects, rather than inertia, dictate roll rates.  Anhedralled wings are rare in aircraft the size of a 172, or any aircraft where cruising comfort is desired.

@RobertGiovianni, Thank you. Isn't lateral stability an Inherent property of High wing? So considering not anhedral to avoid instability and discomfort, yet 0 dihedral on highwing still will give stability right? The point of including An-225 was to compare whether keel affect is more pronounced in heavy aircraft? Or it's anhedral  is just about increasing manoeuvrability? SIMPLY: If there is no dihedral on C172, will the aircraft be laterally stable?

Vertical position centre of gravity is totally irrelevant. It is centre of lateral drag that matters!

Anhedral is not done due to sluggish roll characteristics.  It's done because the effects of wing sweep plus the high wing T junction of wing to fuse, creates excessive dihedral effect, which aggravates dutch roll tendencies. The anhedral is to cancel some of that out.  This is why you see anhedral only on swept wing high wing transports, not straight wing ones.

@JohnK absolutely right about swept wings and high T tails.  Just like the F104.  I would like to try slow flight with that plane upside down.  Yes, straight wings (like the Hercules) are less in need of wing anhedralling, although (like birds) it can also be done in the tail.

@JanHudec  surprised you would say vertical CG is irrelevant, after all, what will the center of lateral drag rotate about?  I found this out by putting a paperclip on the front/bottom of a paper airplane and found it flew worse.  When I put it nearer the wings, it flew much better.

@NoorulQuamar it would be less, but likely flyable.  That dihedral is there so one can take their eyes off the horizon long enough to read a map or reach for a cup of coffee.  Lateral stability is very important for long trips.

Perhaps Cessna wanted to create some more headroom when stepping into the plane?

Please correct the obvious error in "the main function of dihedral is for roll stability in straight line" - dihedral only works in a sideslip. I thought we had settled this long ago already.

@Peter Kampf nice to hear from you.  If dihedral only works in a sideslip there would be a lot of sick people up there.   In straight unaccelerated flight  dihedral is rather effective in damping roll.  Great story about why Lindbergh actually preferred the 0 dihedral (and small tailed) Spirit of St. Louis to be a little "squirrely":  needing to constantly control the plane would keep him awake!.  The value of dihedral in roll damping is proven by the need to hold aileron input (and rudder) in the 172 in a shallow turn.  Higher angles of bank can lead to the inexorable spiral.

Sorry to disagree but roll damping is mostly a function of aspect ratio. For gentle turning characteristics it is the ratio of c${n\beta}$ to c${l\beta}$ that counts.

At least we agree there is a longitudinal axis of inertia.  And I would not disagree that (in a hang glider from its swept leading edge and much lower center if gravity) slipping will produce a strong stabilizing counter-roll.  Many ways to do this in design.

@JanHudec I am sorry but what is centre of Lateral Drag?

For anhedral in a wingspan smaller than the C172, look at the Harrier. Cruising comfort was probably not a consideration...

@NoorulQuamar lateral drag is lateral aerodynamic force due to side-slip.

@user_1818839  The Harrier is a fighter aircraft.  Not exactly the most stable design.  Any others in mind?


text:
How does a pilot report a person (on the surface) in distress?
After a downhill bike ride gone wrong last night.  Around midnight I was climbing up a mountain (to my Jeep) with my bike on my back.
While I was climbing I was thinking about the fact my headlight had an SOS function (I didn't consider using it).  SOS functions of lights are great and all, but then I realized that as a pilot, myself, I am not sure how to report a person in distress on the surface.
As a climber and ROTC cadet, I am well versed in the hand signals, and various ways to flag down airplanes, but as a pilot, if I were to come across someone flashing SOS at night, or flagging me down with a mirror in the day, how would I report their location to get a search and rescue team dispatched?

I would treat an active SOS signal from the ground the same way I would treat an ELT signal on 121.5: Contact ATC (or Flight Service if you're not sure what ATC frequency to use) and inform them of the event.
As with reporting an ELT you should be prepared to tell ATC:

What kind of signal you've observed
(ELT, signal light, signal mirror, "SOS" or "HELP" spelled out with rocks…)
The time you observed the signal
(Ideally you'll report it while overhead & actively monitoring it)
Your location and altitude

Ideally you'll be able to give your location as a GPS fix as SHAF described.
If that's not possible there are other options, in roughly-descending order of accuracy:

A DME fix (radial & DME distance)
A VOR fix (the intersection of two radials from separate stations)
A VOR radial & visual landmark (ideally something on the sectional chart)
While just a radial is not very useful it can be helpful in conjunction with a landmark: "South side of Mt. Greylock, on the 350 radial off Chester VOR" helps narrow down the search area considerably.
A visual landmark based on the sectional chart.

ATC may also ask you to circle the distress signal and ident in order to get a radar fix to supplement any of the above.

It should go without saying (but I'll say it anyway) that a VOR fix is only useful if the radials are not collinear, so use some common sense: Saying "At the intersection of the 082 radial on Chester VOR and the 263 radial on Gardener VOR" isn't useful: those radials define V39 - they're the same line & every point along the way is "at the intersection". By contrast "At the intersection of the 082 radial on Chester VOR and the 194 radial on Keene VOR" is much more useful.

@rbp I've moved the discussion of the various means of determining location  to a chat room as they're beyond the scope of comments. If you'd like we can continue discussing them there.

FWIW, I was specifically taught to use "pan-pan" for a scenario like that, at least to get the controllers' attention; anything more depends on the specific situation. My instructor said that pan-pan is always a good way to relay distress calls or other urgent conditions that don't affect your aircraft directly.
I've never seen any formal document to support that, but emergencies are thankfully rare and formalities are secondary to getting help to whoever needs it.

If you know that life is in danger outside your aircraft, a Mayday is appropriate.

@Simon, that's one radio call you NEVER want to make and you NEVER want to hear.  (Trust me on this!)

Only heard one.  Was a mate of mine got a sudden bang and vibration on a Jet Ranger.  He put it into autorotation and fired out a mayday.  Turned out it was just a piece of blade tape exploding.  All involved said better safe than sorry and he did have a police helicopter overhead about 5 minutes after touching down.

@Simon: I, too, was specifically taught (and just verified that from a textbook) that pan-pan is the proper call for reporting distress of other vehicles (no matter whether air, sea, land; including relaying mayday calls) or persons on the ground or aboard. Mayday is only for calling out an emergency of your own.

This (military air) also this which are the references on http://en.wikipedia.org/wiki/Mayday both say to pronounce it as "MAYDAY RELAY" (which fwiw is not what it says on the Wikipedia page).

@ChrisW My understanding of "MAYDAY RELAY" is that you use it when you're receiving a mayday signal but the agency that would respond to it isn't - that may or may not be appropriate based on the kind of surface distress signal you're getting. "pan-pan" seems generally appropriate for all cases though: You have urgent information to communicate which needs some level of priority, but are not yourself in distress. Either way the important bit is letting someone know and how you go about doing it is largely secondary :)

@voretaq7 Yes. I don't know whether seeing an SOS pattern on the ground should be enough to make you think "MAYDAY" rather than "PAN-PAN". I suppose it should, in theory: because in theory the ground should transmit "XXX" instead of "SOS" if they don't want to be saying "MAYDAY"; but "XXX" isn't well-known and probably not programmed-in to the OP bicycle headlight. Whichever it is, this does seem to me to be a "RELAY".


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Why do modern airliners have only two engines?
In this terrific question we see the advantages of four engines over two. Namely:

Engine out capability: Losing an engine means losing only one quarter of the thrust, rather than half.
Ground clearance.
Drag: Increased yaw control with four engines in an engine-out scenario means that the vertical stabilizer can be smaller, thus reducing drag.
The wing is loaded more evenly.

If that is so, then why don't new commercial airliner designs use four engines?

why don't new commercial airliner designs use four engines? uh, the A380 is old?

Why is increased ground clearance an advantage for a commercial aircraft, which will (barring e.g. ingesting geese when departing NYC) never land anywhere but a paved airport?

Related (Duplicate?): Why does the 747 have 4 engines instead of 2?

Also related: Why couldn't the A380 secure any orders for two straight years?

And also this answer to Has Airbus planned to build a larger version of the A380?

Because there is no need for more engines.

Though one can argue that losing one engine in a twin results in loss of half the thrust, the question is how often does that happen. Engine reliability has improved significantly through the years and engine failures are quite rare today.
I'm not sure how ground clearance is an advantage for quads. For quad engined aircraft using today's high bypass turbofans, the inboard engines would have to be mounted higher for suffecient ground clearance- this is actually a disadvantage as it results in a longer landing gear.
In aircraft, more engines means more (cost and) maintenance and in a way, more things to fail, as there are more subsystems. In effect, there is no great reliability advantage of quads over twins.
One main reason for having more than two engines, ETOPS certification, is no longer relevant. In fact most of the longest routes in the world are flown by the 777, a twin.
The best way is to look at the market- there are no quad engined aircraft under development and most of the aircraft in order are twins (A380 and 747-8s are struggling to get orders). This clearly shows that the customers prefer twin engines over quads.

I'm the same design, choosing four engines instead of two would allow smaller engines, which may be why they are saying that it helps with ground clearance.

4 RR Trent1000s would give significantly more thrust than would 2, and in the same design would be overkill.

How is ETOPS no longer relevant? ETOPS was exactly what allowed twins to start flying those long-haul routes. Before ETOPS, they had to be at least tri-engine.

@reirab I meant that due to ETOPS we have twins in long routes but looks like ended up saying the opposite.

Engines are expensive, maintenance-intensive and heavy. You only need 2 to keep a large plane in the air.
In the days of the 747 regulations required at least 3 engines if you ventured more than 60 minutes of flying time away from a suitable diversion airport (in case the second one also failed). However as reliability of engines increased this got extended with ETOPS certificates.


text:
Why don't transponders have active and stand-by value like radios?
This answer explains how pilots when switching code on transponder should either carefully avoid temporarily squawking one of the emergency codes, or should temporarily put the transponder in stand-by.
Radios (both comm and nav) usually have an active frequency and a stand-by frequency and the pilot selects the stand-by frequency and then activates it with a button, which avoids temporarily selecting different frequency and limits the time when the radio is not receiving.
Why don't transponders have similar mechanism? It seems it would be much more useful for them than it is for the radio.

They do.  Every transponder I've seen has a standby position.

@Simon, a stand-by position on the switch yes. But not a button that would activate the new value only after it has been fully set.

Not all radios have a secondary frequency which you set and then switch to, many older radios have only one frequency.

Just having a short delay (10 seconds) after a new code is set before the transponder uses it, may be enough.

@IanRingrose well yes, the problem only exists on primitive transponders like the one with one knob per digit, precisely because they have relatively simple electronics inside. The knobs are probably wired directly into the sequencing hardware; they're too simple for an automatic 10 second delay.

@Simon That standby mode prevents the transponder from responding to interrogations entirely (your target becomes a primary target only, with no data block). You should generally not set your transponder to its standby mode unless ATC tells you to.

The 10 second delay could be put into the radar software, also with a check that if the plane goes missing the last number is shown even if it was active for less then 10 seconds.

@voretaq7 Well, that's what I was trained to do, and my habit, and ATC have not commented once.  AFAIK, it's common practice so disappearing for 5 seconds is probably no big shakes to them.

@Simon I don't know about it being "common practice" (none of the folks I fly with do it). While I doubt it would be a serious issue in most cases, particularly in relatively empty airspace, it seems contrary to the guidance in the AIM. A sweep in "standby" mode means ATC loses your altitude (and possibly your whole target) until the system interrogates you again which could confuse their conflict alert software. I can't point to a FAR that says "don't do that", but it definitely seems strange to me.

The transponders that have the problem of inadvertently selecting/transmitting "incorrect" (or emergency) codes are old-tech designs. Much like the old-tech radio designs there was no concept of "standby frequency" or "code being entered" - whatever was on the face of the instrument is what it's doing.
Radios of the same vintage have the same interface (e.g. the KX-170b):

The usual solution for the old-tech transponders is to think before you spin the knob. If you were squawking 7701 and told to squawk VFR (1200 in the US or 7000 in most of Europe) you wouldn't turn the right-digit until you'd adjusted one of the other two so you wouldn't inadvertently squawk one of the emergency/alert codes.
(The radar system could still see you squawking the "wrong" code for one or two passes in this situation, but that's a self-resolving problem and it generally doesn't set off any alarms for ATC.)

Modern (push-button entry) transponders do have an "inactive" squawk code in that then new code isn't transmitted until after you're done entering it.  Most also have a clear or one-touch VFR button in case you make an error entering the new code, so if ATC assigned you code 7001 and you inadvertently punched 77 in turbulence you don't need to keep entering a "wrong" code - just hit clear or VFR and try again.

For navigation and communication radios the feature of having a second readout that can be pre-set to the next frequency is useful since the next frequency is usually known in advance. Your next transponder code is a somewhat random number and the moment that you will get it is not as predictable as a frequency change. Therefore there is no need for a pre-set / standby squawk code in a transponder.
Also, in a communication radio, when you pre-set the wrong frequency and cannot establish communication after the switch over, a single button press will bring you back to the original frequency. This prevents prolonged communication loss. This is similar in navigation radios.
For a transponder such a feature has no value, you won't switch back to the previous squawk code.
The problem of inadvertently selecting a special code can be addressed by other means. For example a digital interface that requires confirmation of the selected code before it is activated.

Transponders are more technologically conservative than radios and the old models have a lot of analog electronics in them. You could certainly add the electronics and additional buttons to have them do a switchover the way radios do, and I think newer models can, but the older models are more primitive, which is why you see those instructions to use standby.


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How do you determine the proper rate of descent for landing?
I'm trying to use a simulator to learn to land properly.  One part that I'm finding really tricky is picking a proper rate of descent.  I know I'm supposed to do my best to keep it so I have two red lights and two white lights on the Precision Approach Path Indicator (PAPI), but at the moment I basically am just eyeballing it and adjusting my course whenever the lights aren't right.
I have to assume, though, that for any given airspeed there is a rate of descent I can maintain that will keep me right in the middle of the preferred glide slope for that airport.  I just have no idea how to figure it out.  Is there an application or formula that is preferred for this?  Or is it time to learn Vector Calculus?
PS- I did check this question to see if it related.  But that question is about starting the descent from cruise.  I'm talking about rate of descent for final. I did also check this answer, but it's about using the PAPI/VASI lights.  I'm looking for a formula to figure out the proper rate of descent during final for a given speed.

The question is good and if I weren't on my phone I'd take a crack at the equations, but for practical purposes I'm willing to bet you'll have better luck eyeballing it than you will trying to fly that precise a rate of descent by instruments. Especially if the simulator isn't full-motion.

Are you approaching VFR or IFR? IFR, you can take a look at the approach chart, it will give the descent rate for the glide path depending on groundspeed. For VFR... well, it's called VFR.. you just aim for the runway. It also depends on aircraft used, a TMG will drop from higher altitude and approach with higher descent rate than a SEP.

The formula really shouldn't change if you are accounting for speed, descent rate and optimal descent angle.

You have a good answer, but I will add this:  As a pilot, I only use the VSI as a cross-check in this situation.  I change the pitch to stay on the PAPI and adjust the power setting to keep the airspeed that I want.  The VSI takes care of itself.

Assuming you want a 3 degree glide slope, just take 5 times your ground speed in knots as a starting point.
As an example, approaching at 90kt ground speed in a light aircraft, go for 450feet per minute. at 140kt in a jet, try 700fpm. If you're flying a jet outside of 4 miles, and the controller wants you to keep the speed up at 200kt then descend 1000fpm.
It's not perfect, but it works pretty well for a first guess, and you can adjust as necessary.
Of course, your ground speed is not the same as your air speed, and even for a constant IAS it will likely vary as you descend and the wind changes. Another way to think about this is that a 3 degree glideslope is almost exactly 300ft per nautical mile. If you're 2 miles out and 700 feet up, then you need to descend a bit faster, conversely, if you're at 500 feet, you need to descend slower.
A third related rule of thumb is that your final approach speed (in CAS, although IAS is good enough in most aircraft) is 1.3 times your stall speed in the landing configuration (Vso). So if you stall at 100 knots, you want to approach at 130KIAS.
IFR approaches are all about having an initial guess at these numbers in your head, trying them out, and then adjusting as the conditions require. If you're good at the guesses then the adjustments will be very small.

approach speed in a jet is calculated on the FMS as Vref, not using the 1.3Vso speed.

True, but in practice it will be pretty close to 1.3Vso for almost all types (concord excepted...)

@rbp Typically Vref is defined as 1.3Vso.

For most purposes, if you're flying something with a jet engine, you can probably schwag -700fpm for a 3 degree glideslope and be fairly accurate.  It will at least give you a starting point.  You shouldn't be flying the approach solely off your VSI anyway, but it is useful to determine how large of a correction you are making, or if you're about to bust through the bottom.


text:
What airfoil design is needed for a 4 m wingspan soaring plane?
I’d like to build one that is heavier than a F3J plane and it will be similar to NASA’s soaring plane of the "Autonomous Soaring Plane" project. What kind of airfoil do I need? Simply scaling a normal airfoil would have bad results.

I suggest you ask this on rcgroups.com in the glider forums. Lots of F3J and F3K designers hang out there. The glider crowd is generally very friendly and helpful.

First for those who wonder what F3J is: This is the FAI model aircraft category for thermal soaring.
Quick answer: This answer describes what resources are available on the Net.
Your choice of airfoil depends on the wing loading and the size of the model, because those will determine the Reynolds number of the flow over the wings. Soaring flight requires high lift coefficients, but maybe you also want low drag for sprints between thermals or to avoid being blown away by strong winds.
The description of the NASA Autonomous Soaring Plane gives 15 pounds of mass and a wingspan of 170 in. It was based on a model glider by RnR Products, and there I found the aspect ratio of 19.8 and the wing area of 1545 sq.in. These numbers are not very consistent, but close enough to get an idea.
Thermals are strongest in their center, so it is desirable to fly as tight a circle as possible. Low wing loading $\frac{m}{S}$ and a high lift coefficient $c_{l_{max}}$ drive the minimum turning radius $r_{min}$ down (at a given density of air $\rho$), and the formula is:
$$r_{min} = \frac{\frac{n_{z_{max}}}{\sqrt{n_{z_{max}}^2 - 1}}}{c_{l_{max}}\cdot\frac{\rho}{2}\cdot \frac{S}{m}}$$
Here $n_{z_{max}}$ is the maximum load factor, and the picture below shows that little is gained by increasing $n_{z_{max}}$ beyond 3. The little DFS Habichts help to illustrate the bank angle.

With a wing loading of 6.8 $kg/m^2$ and a mean wing chord of just 23 cm the flight speed at a $c_l$ of 1.2 is 9.5 m/s. At sea level in a standard atmosphere the Reynolds number would be 150,000. The wingtip flies at a Reynolds number of below 100,000. In circling flight with a bank angle of 60° (equivalent to 2g, so you need twice the lift), the Reynolds number would increase to 212,000 for the mean chord and to 140,000 for the tip. If this sounds a lot to you, it isn't. This is a flow which needs highly specialized airfoils.
My recommendation is to try the UIUC airfoil database and select a specific model airfoil with low drag at high lift coefficients and Reynolds numbers down to 100.000. It should have high camber and a thickness of around 12% to keep wing weight down. If you have the lower range of Reynolds numbers covered, you need not to worry about the higher range. You might even consider to use different airfoils over the wingspan, depending on the minimum local Reynolds number. Ideally, you'll find a set of airfoils which have been optimized for exactly this purpose, like the DAE11 - DAE21 - DAE31 airfoils of the Dedalus human powered aircraft.


text:
During the early design stages, what parameters are considered in determining the weight of an aircraft?
What parameters are considered in estimating the weight of an aircraft in the beginning of the design process?

Can you please elaborate? Given that you have tagged aerobatics & aerodynamics, I assume your interested in something particular?

For? Cargo/passenger/fighter/bomber/agricultural/maritime patrol/ aerobatic /micro light? Kit/GA?

Any design starts with a mission profile. As a design engineer, you get the payload, range and speed, and maybe constraints like the maximum runway, and then have to come up with a configuration.
With that in hand, you look what others have achieved before. There are collections of weight data for different designs and their parts, and formulas which combine the main parameters in a way that the weights line up more or less nicely when plotted over the result of this equation. Plug in your new design's number, and you get something wich will be within ±10% of what is realistic. This is called parametric weight estimation (PDF!).
Since you can only consider what you have, you start with the boundaries of the sizing mission:

Payload
Range or endurance
Desired cruise speed and altitude
Operational constraints like runway length, operation from unprepared fields, threat scenario.

EDIT:
@Peter is right: Cost per kilo of airframe and per seat-mile (where applicable) is also a starting requirement, and cost minimization is taken care of by designing the smallest possible airframe which can satisfy all requirements while using proven technology. And parametric sizing only works when based on proven technology.

I guess what you refer to as mission profile in layman's terms would be design goals and intended purpose? Optimization of a design could be considered similar to linear programming you have objectives, variables and constraints. Depending upon a range of factors MTOW could be any off those things.

I guess in today's business world ROI, TCO & operating costs must be factors too.

@Peter: The goal is to find the smallest design which fulfills the requirements, not just any. This, and using proven technology, keeps cost down. Parametric sizing only works when based on proven technology.

When designing, the designers have to take into account:

The amount and type of materials used on the airframe. Many aircraft made nowadays use composite materials because they are stronger and lighter than metals. The engines also play a significant role in this because they have to create a certain amount of thrust without adding too much weight.
They also have to take into account the payload that (amount of fuel, passengers, and/or cargo or other things) that the aircraft will carry.

Weight of the engine(s) might also be significant

@DanPichelman Falls under the materials used. I will add something about the engines in the answer though.


text:
How can I read airport maps when choosing a seat as a passenger?
When I choose seats on an airplane, I usually go for a window seat since I love the view, especially the views of a city on takeoff/landing.
Sometimes I get good a view of the city and sometimes I don't.
How can I look up information on an airport before a flight to choose a side of the plane that will get the best view of the city?
To give a concrete example, I will be flying into DFW soon from the North. Ideally I would get a view of downtown Dallas (East of the airport) when flying in. From AirNav, and the map it links to, I can see the runways at DFW run North/South. If I pick a seat on the left side of the plane will I be guaranteed a view of downtown Dallas?

You can't really, because the runway in use depends very much on the wind at the time of take-off.

@RonBeyer Does the same go for landing?

Yes, of course. The way they come into the airport may change as well depending on what runway they need to use.

FWIW, DFW is far enough (~20 mi / ~30 km) from both Dallas and Ft Worth that you probably won't see either of them, or just a few tiny, faint towers in the distance. The wind direction when you arrive will determine which of the two cities won't be seen from each side of the plane.

@StephenS You may not get good views of Dallas or Ft. Worth, but you can get good views of Texas stadium, I've flown in during a game, and could actually see their giant display screen through the hole in the roof!

There are any number of which side of the plane questions at Travel.SE, but as also noted here, there's no reliable way of knowing what conditions will be. I've even been on flights that landed easterly at LAX.

@GlenYates - if you're seeing Texas Stadium you're also flying back in time! ;D (It's AT&T Stadium and is in Arlington. Texas Stadium was in Irving and demolished years ago)

@NKCampbell Coulda sworn I saw Roger Staubach and Tony Dorsett!, yes of course I meant Cowboys Stadium or now AT&T Stadium.

It seems you already know to look up the layout of the airport, and how to check a map for which direction from the airport you want to look. The piece of the puzzle you're missing is the wind direction.
Aircraft both take off, and land into wind. So it does not matter that you are "coming from the North", if the wind is blowing from the North an aircraft will go all the way round and land on the Northerly runway. So if you were to check the weather and there is a definite Northerly tendency you would want to sit on the Right side of the aircraft.
This is nice and easy when there is a wind, and it is forecast accurately, and you can select your seat close enough to departure to take advantage of this info. Unfortunately there are many things that can throw a curve ball here

Changing wind patterns
Lack of wind / operational reasons to
Multiple runways

About the best you can do is be aware of the prevailing wind, and hedge your bets on which runway will be in use. You'll win some (most?) and lose some. But you'll certainly get a good view some of the time.

"So if you were to check the weather and there is a definite Northerly tendency you would want to sit on the Right side of the aircraft." This would depend on how big of a loop you do around the city, right? Meaning the airplane may stay close to the airport and do a sharp turn or do a big loop around. Is that a flight pattern I can look up?

@quinten I meant on the final approach. What you are looking for are called STARs (Standard Terminal Arrivals). There are many, often for the same runway, and a layman might find them quite difficult to understand (Hell, I have a license and I find them hard to understand!).

"Prevailing wind" is probably the best general bet... Hard to otherwise predict wind direction a month or more in advance. :)

Yes, if the wind is going from the north toward the south, they're going to overshoot the field, fly a J-hook and land facing north.  But you don't know whether they'll make a right J-hook or a left J-hook.  Unless there's a pattern they use conventionally.

@Harper-ReinstateMonica Planes are usually vectored from the NE/SE STARs to the east runways and NW/SW STARs to the west runways, which makes sense. But if one side is much busier at any given moment, they will shift a few planes to the other side to balance them.

In short, the only seats that are guaranteed a good view no matter the approach are - in the cockpit.

You can get airplane layouts for most scheduled commercial carriers online. You can get airport and runway layouts from sources like skyvector. The FAA US Chart Supplement gives the distance and cardinal direction the airport is from the center of its associated city.
As other posters have noted, the issue you will find is that aircraft try to always land into the headwind at the time. While crosswinds are acceptable to a point, tailwinds are avoided if possible. And, most runways can be used for takeoffs and landings from either end of the runway surface.
Just remember one thing about aircraft and airports. Getting an airplane onto a runway is a three step process. They are:

Arrival to the area. This can be a simple decent from cruise or a charted arrival procedure.
Approach to the airport. This can be a charted approach or an entry into a standard traffic pattern.
Landing. This is a decent on final approach from the traffic pattern, circling approach or on the glideslope/glidepath of an instrument approach or VASI onto the runway surface.

All of these can be to or from different directions for the same flight. For example, an arrival from the East, to a Northbound approach, ending in circling the airport a half to 2 miles from the airport for a Southbound landing.
In the case of Dallas, the winds come predominantly from out of the South. So, aircraft will land from the North to the South. ATC will route all aircraft around the DFW airport to approach their landing airports from the North regardless of their origin or original heading. On the occasion that the wind is coming from out of the North (which is not as often as the South), ATC will reverse the flow of traffic to approach their landing airports from the South. I term it the “landing airport” because most of the airports in and under the DFW Class B airspace will take directions and follow the lead of KDFW, landing in the same direction to accommodate the very busy airspace (most, but not all of the time). Of course, the smaller and slower the  aircraft, the tighter the route around the airport will be. Some routes (traffic patterns) will be less than a mile away from the runway of landing.

Thank you for the details on the landing process, that gives me some really helpful context


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Why does the angle of descent increase in a constant headwind while decreases in a sudden encounter with a headwind, in a descend?
I'm currently studying aerodynamics.
I have realized that a sudden encounter with a headwind during descent
will result in the aircraft generating more lift, thus angle of descent decreases.
I haven't studied the descent in a constant headwind, but through research I've come across that a constant headwind during descent will increase the angle of descent.
This does not make sense. Shouldn't the angle of descent decrease in both situations? Will appreciate it if someone could explain this.

you will find this a lot of the times in aerodynamic books/formulas, that people tend to neglect a very important aspect: aerodynamic formulas/principle are usually for steady-flow-state.. that is in unaccelerated,unchanging conditions. Adding gusts, control surface changes or accelerations will sometimes produce cotradictory results (like in this case). Just wait until you tackle elevator/trim changes... used to drive me mad

For an aircraft descending from a high altitude, the angle may also change during a single descent with constant headwind. But I see that that's a different effect than the one you were asking about.

You have to consider the difference between rate of descent and angle of descent.
The rate of descent is expressed in distance/time, usually feet/second. This is determined by your airspeed and trim configuration. The ground speed does not affect this, only airspeed.
The angle of descent is the angle the plane is flying with respect to the ground.

When flying into a steady headwind the ground speed will be lower at the same airspeed. But the descent rate will be the same. So if you're descending at the same rate, but moving forward at a slower rate then the angle will be steeper.

On the other hand, a transient gust of wind will temporarily increase the airspeed. When the gust hits it will take a moment to overcome the inertia and slow the aircraft. So momentarily your airspeed will increase but your ground speed stay the same. An increase in airspeed will mean more lift, thus a lower descent rate at the same forward ground speed. A lower descent rate at the same ground speed will yield a shallower angle.

Thank you. I thought no one would answer it and had asked a captian about this and his answer was similar to yours. He had said that the descend in a headwind will occur later compared to nill wind and the "destination point" will be the same, thus the headwind will mean a steeper descend angle. I always took the angle with reference to the straight line ontop of the airplane instead of the ground reference, but your answer gives more clarity. Much appreciated.

Good artwork.  Illustrates the problem very nicely!

Consider descending in zero wind, trimmed to an airspeed of 80m/s (288km/h) and a sink rate of 2m/s. You won't touch stick, trim tabs or throttles during the descent, but you will encounter a headwind at a later time. For now, ground speed is equal to airspeed and the angle of descent is 1:40.
You suddenly encounter a headwind of 20m/s. Ground speed remains at 80m/s due to inertia; Airspeed rises to 100m/s. The rise in airspeed increases lift and reduces sink rate to 1m/s. The angle of descent is now much shallower, at 1:80.
After a couple of seconds, airspeed bleeds off and the aircraft resumes its trimmed state at an airspeed of 80m/s and a sink rate of 2m/s. This time, the ground speed is only 60m/s due to the headwind and the angle of descent is now 1:30.

But that's only if we refer that angle to a ground observer. For example, a ground-based observer with a wind of 40 m/s will always measure an angle of descent of 90º for an airplane gliding upwind with an airspeed of 40 m/s, irrespective of the glide ratio of that aircraft... However, if the frame of reference is the mass of air, as is usual in aerodynamics, the angle of descent is unaffected by the wind...

@xxavier - You only talk in angles when flying an approach or takeoff (obstacle clearance) or in a glider. In all these cases, glide angle over terrain is what matters, so angles are always referenced to ground. I agree that if it weren't so, this question would be pointless.

@ Rainer P. Yes, in the case of a glider flying low, the reference is, for obvious reasons, the ground, but that seems to me a very special case, not mentioned, even indirectly, by the OP...

@xxavier - The only instances where I needed to calculate such angles were like: If I encounter headwind on ILS, will my aircraft deviate up or down? If I'm in a glider 40km out, will I make it home? Will I clear that hill at the end of the runway? Angles are always relative to ground.

Not in the OP's query. He doesn't mention a ground reference, not even when he speaks about the wind, since it's obvious that a plane, when crossing a wind shear interface, would suffer a transient perturbation in airspeed and descent rate, but things will soon become normal again, with all flying conditions unaltered in the new mass of air. The OP seems to believe that that transient perturbation persists, something that is wrong...

@RainerP. I agree with your answer. I m not disputing that. My query is, compared to nil wind, will a constant headwind make the angle of descend shallower or deeper?

Apart from transient effects, that are short-lived as such, for example in that 'sudden encounter' that you mention, the angle of descent of a gliding aircraft is not affected by the wind...

That is correct as observed in the aircraft (i.e. a flightpath vector in a HUD), but from a stationary outside observer's viewpoint, the descent angle absolutely does change. Or, in a very practical application, if you need to cross a given fix at a particular altitude and airspeed, the effects of headwind and tailwind on your descent angle in space play a significant role and have to be accounted for.

@Ralph J   The question, as stated by the OP, is not related to practical flight, but just to aerodynamic considerations. Hence, any ground reference is out of place...

except for an obscure certification climb requirement in still wind (which exists only for funny political reasons) can you find any usefullness of calculating a climb/descent angle using the moving mass of air as reference instead of the ground?

@ Radu094. It's not a matter of usefulness, but of answering the query of the OP in its terms. Besides, yes, calculating the descent angle in relation to the mass of air is quite useful. It's exactly the angle determined by the L/D of the aircraft...

I've never heard of anyone ever referring to an angle of descent that did not concern a ground reference. In your theoretical concept where the "angle" is referenced to the mass of air there is no such thing as headwind. The word "headwind" presumes a ground reference.

Not if a transient airspeed perturbation caused by external reasons –a relative movement of the mass of air– is contemplated...

@TomMcW I have seen both, as well as an equation relating the two. But the OP's comments indicate that the ground-referenced angle was the one desired, so the air-referenced angle is relevant only insofar as it helps us find the ground-referenced angle. (And that is why yours is the accepted answer.)


text:
What does the sign "Caution your blast" mean?
At London City Airport (LCY) there exists a "CAUTION YOUR BLAST" sign. This isn't one I've seen before. What does it mean?

I'm fairly sure that sign is beside taxiway C*, and as you can see from the aerodrome chart it is right next to the main apron. Aircraft holding in this position have the main apron directly behind them.

The sign is instructing pilots to use the minimum thrust necessary to move off from that position, as there could be personnel, vehicles etc on the apron. As this is a bit of a mouthful "Caution your blast" is used.
This is further backed up by the aerodrome textual data which states:

Pilots are requested to use minimum power when manoeuvring on and off parking stands and when entering the runway.
  The use of minimum power is particularly emphasised when holding at the the entry points to the runway and when
  entering the runway.

The other hold points around the apron seem to have a similar problem Taxiway B has the same sign. Perhaps the others do too.

(Image source: https://www.airlinequality.com/review-pages/gallery-airline-reviews/)

* This was based on personal memory of seeing this exact sign, and of being aware at which hold point we were at. I went and checked using google earth/street view. There is a good view from the terminal however the sign itself is obscured by an aircraft. However you can clearly see the building opposite from the original picture, and so the position for Taxiway C lines up.

Jet aircraft are legendary for generating enough exhaust force behind them to blow over people, baggage carts, smaller aircraft, or any other loose object.  An extended NASA safety reporting system discussion of the hazard is at https://asrs.arc.nasa.gov/publications/directline/dl6_blast.htm.  Boeing further describes blast details at http://www.boeing.com/commercial/aeromagazine/aero_06/textonly/s02txt.html, noting that the hazard extends hundreds of feet behind the aircraft's engines.  When a jet has been stopped and needs to start moving, the crew needs to set power to reach "breakaway thrust", which is substantial for a large aircraft.  Once moving, power can be reduced - but there will still be a blast hazard close behind a taxiing aircraft.  In the environment described in the LCY question, all the runway entry points are likely to have stopped aircraft that need to go to breakaway thrust to start moving onto the runway, and that could easily cause control problems for aircraft moving on the apron behind them.


text:
Where is the best place to perform a run-up at a busy airport?
If you wait to perform a run-up at the end of a taxiway at a busy airport you will probably not make many friends.  Some airports may have designated run-up areas or have runways designated for general aviation but at those that don't would it be acceptable to do a run-up on the ramp before you taxi?

If you at an unfamiliar airport, you can ask the FBO or your instructor. At my airport we can do run-ups at any unoccupied part of the ramp (just don't blow rocks/dirt at aircraft/people).

Most airports have a place to pull off left or right near the end of the runway to allow turning towards the runway (maybe not quite perpindicular at small airports) for the runup before pulling up to the hold short line. If not, there is typically enough room to at least turn & hold short while running up to not blast the guy behind you.
If you have a problem after that, you can likely get clearance to taxi down the runway and pull back nearer to where you started to find an FBO for help. Or back to parking if the FBOs are closed. Non-towered airport, wait for the runway to clear, then announce and pull out and taxi to where needed.
At smaller airports, there will be a place, maybe nearer parking and parallel to the runway, where you can runup before taxiing, or backtaxiing, to the end of the runway for takeoff.  9B1, Marlboro, MA, is one such airport. The paved runup area is above the word MARLBORO, or out in the grass north of the runway.
https://www.google.com/maps/place/Marlborough,+MA/@42.3435127,-71.510151,255m/data=!3m1!1e3!4m5!3m4!1s0x89e38b0e6861ee6d:0xc7e9aa4b55f5afc4!8m2!3d42.3459271!4d-71.5522874

In my humble opinion it is best to ask the FBO for their practices or do it at the ramp with precautions as not to hurt or disturb anyone or anything.
On the Taxi way you might run into difficulties returning to the ramp in case something does not look or perform right during run-up. When in dout I ask Ground for advice.

At the end of the taxiway is better, as plugs can foul during a long taxi out to the end of the runway. And at some airports it is pretty long. Runup at the end gives a last chance to get the engine hot and clear them up prior to taking the runway.   At Nantucket for example, if you are parked near the intersection of 15 and 24, but are taking off to the northeast on 06, then you would taxi almost the full length of 24, past the airport and FBOs and other general parking.  Plenty of time for plugs to foul, especially if you had forgotten to lean out the mixture while taxiing, for example.


text:
Would a slower speed and lower altitude reduce fatal incidents?
If it became plausible to fly commercial aircraft much lower in the future (due to developments in technology and airway regulations permitting it), say at a standard height of 5,000ft, but with a slower speed - would that prevent / greatly reduce fatal incidents?
In other words, if an aircraft goes down at 5,000ft and 150mph, it's more likely to have survivaility vs 30,000ft at 500mph.

Considering 1,500 feet and 100mph (say, in a Cessena 152) can be pretty deadly in an uncontrolled crash, whatever makes you think 5,0000ft/150Mph is any safer than 30,000ft/500mph?

I suggest you check out this question for some great information about the physics of crashes. The short version is that the limiting factor is the human body, not technical or procedural considerations. You might also want to consider that fatal airline incidents are already so rare that it would be hard to even define and measure a "great" reduction.

Altitude is not a liability; it is an asset!  Speed is life; altitude is insurance.

@abelenky while the question can looks like naive and most users here can  labels it as "too obvious" it's a valid question. It's like you go to physics SE and ask why apples falls. I can consider to close it only if it's a duplicate (a nearly question is also pointed by Pondlife)

@Cloud You are trying to fix a non-problem. Air travel is remarkably safe and making it slower and more expensive in an attempt to make it slightly safer is a bad tradeoff.

Most really bad accidents happen at ground level -- either on takeoff, approach, or landing. It's quite rare that something really bad happens at cruise altitude, and even more rare that the altitude had all that much to do with it (in a negative way). Flying over weather at 40,000' +/- is safer than flying through it at 5,000' +/-.

@Ralph J: And that goes double for mountains - around here something that travels at 5000 ft MSL would be a subway :-)  I can't offhand recall an airline accident where "too much altitude/speed" was a factor, and several - the "Gimli Glider", Air Transat Flight 236, &c - where sufficient altitude & speed prevented a more serious one.

@abelenky Even by the standards of this SE, that ("because accidents are rare") is an utterly absurd basis for deciding that something's off-topic.  It's a perfectly good question, with the scope for much useful illumination in the answers, at least by people who think that the purpose of this site is to share their knowledge and insight with those that don't have it, rather than to sneer at them and shut them down for not having it.

@DanieleProcida Unfortunately, his attack was quite personal. I have received personal messages from him and he has gone through all of my questions and down-voted them. He just doesn't like me for some reason.

@Cloud If you feel you are being personally targetted by someone, then flag the content for moderator attention and describe the issue. That's what the moderators are here for.

@Cloud Why would such a limitation have any positive impact at all?

Apart from mid-air collisions, people tend to die in aircraft at very low altitude and speed :)

In addition to the excellent answers already given, airplanes typically use less fuel cruising at high altitudes than they do at lower ones, and so airlines have a vested interest in flying as high as practical to reduce their fuel usage as much as possible.

On the other hand the US Goodyear blimps survived 2 major crashes including a hull loss and 1 airborne attack, with only minor injuries. Key seems to be never going above 40 kts.

Speed doesn't even kill on the highway. Why would it kill in the air?   Yes I know that is a bold claim: what kills is speed differential.  You get these church mice on the highway going 50 "for safety" while the rest of the flow is going 70, it forces thousands of people per hour (highway traffic count x 50 / 70) to maneuver around them in low-risk but numerous maneuvers - sooner or later 50 and 70 traffic collide: with energy of 70^2-50^2 = 49^2. Because they cowardly abdicated their safety responsibility to random others.

Preventing accidents isn't the primary concern of airlines. Even if an airline did this, passengers would be pissed because flight times would be MUCH longer. No one wants that. This is a ridiculous question.

Slower flights means less route capacity.  To offset that means more flights, more takeoffs/landings, more Tenerifes:(

A 30-knot collision can be fatal.  A 10-foot fall can be fatal.  The application of this to air travel should be obvious.

@user71659: But on the third hand, what is the Goodyear blimp if not a really big airbag?  Not to mention a rather inefficient parachute :-)

Obligatory: It's not the fall that kills you. It's the sudden stop at the end.

@sgroves: note that the question isn't whether this is a reasonable tradeoff, it's just whether it could reduce fatal accidents, even by the smallest margin even at ridiculous cost.  The top answer points out that failure rater per flight-hour means that the answer is still an emphatic "no".

When I learned to fly gliders, there was a joke about a mother saying “fly low and fly slow!” (actually it was in Italian, in English it even rhymes...)

@PeterCordes That makes sense. It's certainly an interesting question.

@WalterTross Not just in Italy, and not just a mother, and not just about gliders... :-)

I'd like to answer this question by debunking the premise of the question: that most plane crashes happen when planes fall out of the sky, and that it's like rock climbing where the higher you are, the more likely a fall will kill you.  While it sounds believable, it's almost entirely false, and since it isn't diving out of the sky that kills you, lowering the altitude doesn't really help flights become safer.
Planes don't need speeds of over 300 mph/500 kmh ground speed to be deadly. A car accident for comparison is generally considered to be very likely fatal above 80 mph/130 kmh  (source: DFT London).  Even plane crashes at takeoff and landing speed of around 150 mph/240 kmh can be difficult to survive just due to physics. Every one to three years there's a plane that crashes on takeoff or landing with almost no survivors like TransAsia 235. The most deadly accident ever happened when two planes collided as one was going about 160 mph/260 kmh and the other was almost stationary!
Even if you could easily survive a 150 mph/240 kmh collision, a ground speed of 500 mph at cruise doesn't mean the plane would crash land at 500 mph. Planes don't just dive out of the sky, gaining speed to 500+ mph/800+ kmh (except in total structural failure and breakup, but then you're a goner even at 150 mph). Even in extreme circumstances like loss of all flight controls in UA 232 the aircraft could slow to about 250 mph/400 kmh before crash-landing.  The "Miracle on the Hudson" aircraft slowed a lot after engine loss as it descended towards the river.  Even the dive of Alaska 261 caused by jammed flight controls could be slowed to about 250 knots using air brakes and flaps.  So the actual crash speed for high altitude incidents is usually less than 300 mph even in catastrophic incidents, which you could easily also achieve after an incident at lower altitudes and speeds.
Any serious changes to aircraft have to make enough of an improvement to be worth the disadvantages involved.  When we're talking about things like making flights slower, that's a serious disadvantage.  Probability per flight hour that an engine or flight controls will catastrophically fail is small but very real number in hazard analysis and so longer flights have a higher chance of an incident.  If the cruise portion of a flight takes twice as long, is that portion now twice as safe per minute to compensate?
Edit: As Martin James and Milwrdfan have pointed out, flying lower and flying slower both increase the amount of fuel you need per trip, which lowers the amount of passengers you can take.  This would increase the number of planes in the air which would probably decrease safety per passenger as well.
Finally, the most dangerous parts of a flight are takeoff and landing. Nearly half of accidents occur during final approach and landing, and only 10% occur in cruise (source: Boeing).  If the past few years are any indication, you're about as likely to have your plane damaged by terrorists as to crash during an incident in cruise.  So you're making every flight lower and slower to help less than one accident per year.
Now that this is the accepted answer, I should point out that Dave has some very good points in his answer about the particular dangers of lower altitudes like weather and glide distance.
So in summary, the premise that cruising at 150 mph and 5,000 ft AGL is relatively safe, while cruising at high speed and high altitude is relatively dangerous, is a faulty assumption. So you don't have much to gain by lowering the speed and altitude.

Cruising at reduced speeds implies cruising for longer time, increasing the odds of incidents during cruising. There's something self-referential about that :)

Well, given that X pax need to travel from A to B, flying slower means more flights are required to carry the same load.  That means more takeoffs/landings....

@MartinJames That doesn't add up. Each takeoff+landing gets the same amount of people to their destination. There's going to be more planes doing the same number of takeoffs and landings (i.e., more planes in the air).

It would likely create a more deadly situation.
In aviation altitude is your friend. Generally speaking altitude in the case of an emergency buys you time to work the problem. Generally you want to be as high as practical for the aircraft in question. Altitude also buys you glide distance to find a suitable landing location in an emergency.
Airplanes also fly high to fly over the weather which is far safer than flying through it at 5000 ft.
Historically airplanes once did fly low and slow (in the propeller days) and there has always been a move to make them fly higher and faster, its hard to quote a direct cause and effect as technology has gotten far better but there is a clear trend that aviation has gotten far safer the higher we have flown.
Perhaps more importantly one of the things that makes commercial aviation attractive is that you can fly far and fast something that is only achieved at high altitudes. The current airway system and technology already permits 150Kt 5000Ft. traffic, just ask any general aviation pilot... but we all want faster, higher flying planes...

There's a recent question about minimal altitude needed to avoid a famous disaster exemplifies why you do want to fly high to fly safe

Not all GA pilots want to fly higher & faster, though.  If you like flying into short backcountry strips, you tend to really appreciate a low stall speed :-)

@jamesqf very true! but Im still relegated to an archer and watching my buddy depart in his 'toga or the local king air whiz buy makes for some real ramp envy.

@Dave: Different strokes.  My envy was more usually directed towards Maules, Citabrias, and the like.  But then, I drive a 15 year old Miata instead of a newer Porsche, BMW, or American muscle car.

@jamesqf different strokes indeed, although I do drive a '78 911SC.... Then again I've been lusting for a Mooney, too bad they wont bring back the PFM

In aviation altitude is your friend. Well, that has to moderated: in a non-pressurized airplane, it can also be deadly, due to hypoxia!

@kebs I did note " to be as high as practical for the aircraft in question" understandably hypoxia is an issue but this is mostly about the legal and proper operation of an aircraft. Climbing above service ceilings or failure to use oxygen when necessary could be a question on its own.

The only commercial aviation accident I can think of which might have turned out differently had the aircraft flown at a lower altitude (which is not to say that it would have turned out differently, or that it's the only one that might have) is Swissair 111. Had they been closer to the ground initially, it's possible that they might have been able to land the aircraft before the fire destroyed critical flight control systems and wiring to the point that the aircraft was uncontrollable, given how late in their descent they lost all control of the aircraft. (IIRC, a few thousand feet AGL.)

Other answers have explained why height is a good thing. I don't want to elaborate on that, but to focus on one aspect of the question's reasoning.
It's implicit in the question that a falling object gains velocity as it falls, and hence that an aircraft falling from a greater height will reach a greater (and more destructive) velocity at the point of impact.
This however ignores the fact that falling objects in an atmosphere will reach a terminal velocity. It takes only a few seconds for an object to get very close to its terminal velocity in the earth's atmosphere.
A plane falling from a great height and a plane falling from a fairly small height will both, quite quickly, be at similar terminal velocity. A lower height won't make much of a difference.

That's a good point !

This is true for objects in freefall, but if your airplane is in freefall, you're going to have a bad day anyway.

To add to the several good answers here consider the human implications of slower travel: crews will be at the controls for longer. But tired crews are a significant factor in risk.
In principle you could land to swap for fresh crew (and take on fresh consumables), but take-off, taxi, and landing are the most dangerous parts of a flight.
(You could also carry spare crews, but that represents volume and weight that you can't use for paying cargo or passengers. Similarly the extra consumables required by long flight times will eat (heh!) into the number of seats you can sell.)
In short operating in this way could lead to more danger rather than less.

For that matter, passengers will spend more time at risk of suffering a medical emergency requiring prompt treatment, plus more of the general stress many people experience while stuck in a metal/composite tube.

Along the same lines, range would be reduced by the lower airspeed and denser air, so we'd be back to 1930s era several stops for long-distance flights.

On the contrary, it would increase fatal accidents. Airplanes require airflow over the wings in order to fly. Once that airflow gets too slow, it detaches from the wing and becomes turbulent. This is an effect called aerodynamic stall. When that happens, the wing loses lift and can no longer hold up the airplane.
From high altitudes, in most airplanes it is normally very easy to recover from a stall and all pilots practice doing this. Simply pitching the nose of the aircraft downward will trade some of the aircraft's altitude for airspeed and the stall condition will be recovered. However, if you're flying low, you don't have as much extra altitude to spare and you're more likely to crash into the ground before you can recover from the stall. So, by flying low and slow, you have much less airspeed margin to work with before stalling and also much less time to recover from a stall should one occur.
In addition to the wings being less effective at low airspeeds, the aircraft's control surfaces are also less effective (and, if you fly too slowly, those can stall, too.) The slower you fly, the less control you have in all 3 rotational axes. This further reduces flight safety by reducing the pilot's ability to maneuver the airplane.
Thus, far from decreasing fatal accidents, flying low and slowly is actually one of the most dangerous things you can do in an airplane.

As far as the question about "going down" from 150 mph at 5,000 feet vs. 500 mph at 30,000 feet, in the best case, this will have no effect on survivability. In most cases, it will make survivability much worse. In the case of the aircraft becoming completely uncontrollable without any possibility of recovering controllability, the situations will be the same, as everyone will die in both cases. There is little-to-no survivability in either case. However, the aircraft suddenly losing all controllability while cruising is (thankfully!) an extremely rare failure mode for airplanes.
Most incidents that happen during cruise (which are already a relatively small minority of aircraft accidents) are aided by having more speed and altitude. As discussed above, the speed keeps the airplane flying and makes it more controllable by the pilots. Altitude buys the pilot reaction time.
Consider, for example, the case that all of the airplane's engines lose power. If you're flying 150 mph at 5,000 feet, you have only a few (maybe 3-5) minutes before you'll be on the ground, one way or another. Since you're only flying at 150 mph, you're unlikely to be able to safely reach a runway much more than about 10 miles away. Now consider the same engine failure, except at 500 mph and 30,000 feet. You now have probably over 20 minutes before you'll be on the ground and you're moving 500 miles per hour. Any runway within about 100 miles is now potentially an option for a safe landing and you also have a lot more time to try to get the engines running again before reaching the ground as well as to alert ground staff to have emergency equipment waiting for your arrival. The latter scenario is much more likely to be survivable. This is especially true if the aircraft is currently flying over rough terrain where a crash landing would not be survivable.

As my (Spanish speaking) instructor used to say often, "velocidad y altura conservan la dentadura", which can be roughly translated to "altitude and speed will keep you your teeth".

Good answers here already but I'd add, flying lower and slower makes flying more dangerous in that the aircraft is MUCH more susceptible to low altitude atmospheric conditions. If you have ever travelled in a commuter plane at low altitudes on a windy cloudy day you will appreciate how bumpy the ride is.
Flying high gets you up above those ground level effects and as such there is much less stress on the air-frame.
Further, at low altitudes you are far more likely to hit birds or slow moving light aircraft.
Your premise of being higher and faster being more likely to kill you is actually false. It does not matter if you auger in at 150km/hr from 5K or 500km/hr from 35K, you are just as dead. It's not the fall that kills you. it's that awkward hitting the ground part.
Flying lower may make the horrific and terrifying journey to your end a little quicker though, and identifying the remains might be easier.

I'm not at all sure identifying the remains would necessarily be easier; see Daniele Procida's point on terminal velocity.

@MichaelKjörling that is why I said might.. but it was tongue-in-cheek

Well, the tongue-in-cheek part must have gotten lost flowing through the intertubez.

It's not the wind that makes the ride bumpy, it's usually the thermals (i.e., vertical wind as opposed to horizontal wind). Wind gets stronger with height.

@MartinArgerami yes I more meant blustery winds changing speed and direction which are more of an issue closer to ground.